JPH0828590B2 - Leakage electromagnetic wave shielding structure - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leakage electromagnetic wave shielding structure, and more particularly to a leakage electromagnetic wave shielding structure for preventing leakage of electromagnetic waves from a joint between a metal case accommodating an electromagnetic wave radiation means such as a high frequency transmission circuit and a lid. .

[0002]

2. Description of the Related Art In a first conventional example of this type of leakage electromagnetic wave shielding structure, as shown in the sectional view of FIG. 4, a metal case 23 and a metal lid 22 are joined and sealed at a joint 24. Here, in order to prevent electromagnetic waves leaking from a high-frequency transmission circuit (not shown) installed in the housing portion 25 from leaking through a minute gap of the joint portion 24, a groove 26 is formed around the metal case 23. Shield rubber 2 provided and described later
1 is set. This shield rubber 21 is a metal lid 2
2 are squeezed in a state of being screwed to the metal case 23 at a predetermined interval, and the metal lid 22 is crushed over the area of the contact portion 24A.
The surface is closely attached to prevent the leakage of electromagnetic waves. The material of the shield rubber 21 is silicon rubber impregnated with silver or copper powder so as to have conductivity. Therefore, the shield rubber 21 maintains conductivity with the metal lid 22 and also has adhesiveness due to the elasticity of the silicon rubber. It is kept.

Next, as a second conventional example shown in FIG. 5, as shown in Japanese Patent Laid-Open No. 61-269892, a low leakage current from a radio wave leakage passage 33 between a microwave oven main body 31 and a door 32. In order to attenuate electromagnetic waves of high frequency (2.45 GHz) to high frequencies (9.80 to 12.25 GHz), a low frequency electromagnetic wave absorption gasket 34 and a high frequency electromagnetic wave absorption gasket 35 are inserted side by side. ing. 30 with these two electromagnetic wave absorption gaskets
The amount of attenuation is about dB / cm.

The third shown in FIGS. 6 (a) and 6 (b)
As a conventional example of the above, as shown in Japanese Utility Model Laid-Open No. 56-56195, as shown in FIG.
A ring-shaped sheet 44 is arranged in the opening 42 between and, and hard ferrites 49 and soft ferrites 50 are embedded in the ring-shaped sheet 44. Further, in FIG. 6 (b),
The soft ferrite 50 in which the magnet 51 fixed to the container body 41 is embedded is provided between the openings 42.
The lid 43 is magnetically attached to maintain the adhesiveness.

[0005]

However, in the first conventional example, the conductivity of the shield rubber is limited, and the length of the contact portion between the metal lid and the shield rubber is also limited, so that severe electromagnetic wave shielding is performed. There are insufficient drawbacks to be effective.

Further, the second conventional example has a drawback that attenuation is limited to a specific frequency band in order to attenuate electromagnetic waves in the oscillation frequency band of a magnetron of a microwave oven or the like.

Further, in the third conventional example, since the annular sheet and the soft ferrite are interposed in the gap having a short length dimension, there is a limit to the adhesion between the container body and the lid, and a high shielding effect is expected. I can't.

[0008]

A leakage electromagnetic wave shielding structure of the present invention covers a metal case having a first semi-groove portion in an outer peripheral portion which houses a means for radiating an electromagnetic wave and forms an open surface, and the open surface. A metal lid attached to the metal case to form a closed space by engagement with the first half-groove,
An elastic shield rubber fitted in the space and incorporating a blocking filter having a plurality of electromagnetic wave attenuation functions for the leakage component of the electromagnetic wave.

A plurality of magnetic powders are impregnated into the peripheral edge of the conductive rubber forming the base of the shield rubber at wavelength intervals of n / 4 (n is an odd integer) of the central frequency band wavelength of the leakage component of the electromagnetic wave. A piece of rubber is embedded to a specified depth.

The magnetic powder is ferrite powder.

Also, when the leakage component of the electromagnetic wave enters the outer peripheral portion of the shield rubber fitted in the space portion while being divided into the clockwise direction and the counterclockwise direction, the electromagnetic wave leakage component The distance between the electromagnetic wave input joint portion and the electromagnetic wave output joint portion in the space is set so as to have opposite phases at the composite point.

[0012]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of the present invention.
FIG. 2 is a structural explanatory view of the shield rubber 1 in FIG. The leakage electromagnetic wave shielding structure of this embodiment has a storage portion 8 for storing an electromagnetic wave emitting means (not shown) such as a high frequency transmission circuit.
And a metal cover 4 having a semi-groove 9A having an L-shaped cross section in the peripheral part and a semi-groove 9B having a U-shaped cross-section in the peripheral part fitted to the metal case 5. Surrounded by a half groove portion 9A (metal case side) and a half groove portion 9B (metal lid side) that generate a closed space in a state where the metal case 5 and the metal lid 4 are fitted, and the half groove portions 9A and 9B. And the shield rubber 1 which is compressed and fitted into the space. The shield rubber 1 is composed of a conductive rubber 2 and a plurality of ferrite rubbers 3 embedded in the peripheral portion of the conductive rubber 2 at predetermined intervals.

Next, the operation of the shield rubber 1 with respect to high frequency leakage electromagnetic waves will be described with reference to FIGS. 1 and 2. In FIG. 1, the electromagnetic waves entering from the inner joint portion 6 leak in the clockwise A direction and the counterclockwise B direction. First, the leak wave in the A direction is the contact portion between the conductive rubber 2 and the metal lid 4 and the ferrite. The rubber 3 is sequentially leaked to reach the outer joint portion 7. On the other hand, a leak wave in the B direction similarly leaks the contact portion between the conductive rubber 2 and the metal case 5 and the ferrite rubber 3 in sequence and reaches the outer joint portion 7. Here, the electrical wavelengths from the inner joint 6 through the conductive rubber 2 to the first ferrite rubber 3 are λ2E and λ2F, and the electrical wavelengths between the plurality of ferrite rubbers 3 are λ2A to λ2D, respectively. The electrical wavelengths in the depth direction of each ferrite rubber 3 are λ1A to λ1E, respectively. The electrical wavelengths of λ1A to λ1D are selected to be approximately 1/4 wavelength. The electrical wavelength ¼ wavelength is a value that takes into consideration the wavelength shortening rate of the ferrite rubber itself. The electrical wavelengths of λ2A to λ2D are preferably long contact surfaces and selected to be an odd multiple of ¼ wavelength. By adopting this configuration, the part of the ferrite rubber 3 has a high impedance and the part of the conductive rubber 3 has a low impedance. Therefore, the leaked electromagnetic waves that reach the outer joint portion 7 by this number of steps are attenuated. Also, λ1A to λ1D
The stop band width can be widened by gradually changing the electrical wavelength of the. Further, since the ferrite itself also has a function of absorbing electromagnetic waves, the amount of attenuation increases. Where λ2E
It is more effective if the electrical wavelengths of λ2F and λ2F are shifted by ½ wavelength, and the residual leaky wave in the A direction and the residual leaky wave in the B direction are combined in opposite phases at the outer joint 7. Therefore, as shown in FIG. 1, the cross-sectional shape of the half groove portion 9A of the metal case 5 is L
By making the mold into a U-shaped cross-sectional shape of the semi-groove portion 9B of the metal lid 4, the inner peripheral distance from the inner joint portion 6 to the outer joint portion 7 of the formed space portion is clockwise and counterclockwise. And a structure capable of ensuring the above-mentioned 1/2 wavelength electrical wavelength. The shield rubber 1 is formed into a substantially cylindrical shape as shown in FIG. 3, and the metal lid 4 is screwed to the metal case 5 and compressed into the space formed between the half groove portions 9A and 9B. Inset.

[0015]

As described above, in the leakage electromagnetic wave shielding structure of the present invention, the shielding rubber incorporating the function of the blocking filter is formed in the closed space portion which is formed by the metal case and the half groove portion of the metal lid to give a long contact distance. By providing it, there is an effect that a high leakage attenuation amount can be secured and a wide leakage attenuation band can be secured.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a structural explanatory view of the shield rubber shown in FIG.

3 is a perspective view of the shield rubber shown in FIG. 1. FIG.

FIG. 4 is a cross-sectional view of a first conventional example.

FIG. 5 is a cross-sectional view of a second conventional example.

FIG. 6 is a cross-sectional view of a third conventional example.

[Explanation of symbols]

 1 Shield Rubber 2 Conductive Rubber 3 Ferrite Rubber 4 Metal Lid 5 Metal Case 6 Inner Joint 7 Outer Joint 8 Storage 9A, 9B Half Groove

Claims (4)

[Claims] 1. A metal case having a first half-groove portion in an outer peripheral portion which houses a means for radiating an electromagnetic wave and forms an open surface, and the first metal case which is mounted on the metal case so as to cover the open surface. A metal lid that forms a closed space portion by engaging with the half-groove portion, and an elastic shield rubber that is fitted in the space portion and that incorporates a blocking filter having a plurality of electromagnetic wave attenuation functions for the leakage components of the electromagnetic wave. A leaky electromagnetic wave shielding structure comprising: 2. A magnetic powder is impregnated into a peripheral edge portion of a conductive rubber forming a base of the shield rubber at a wavelength interval of n / 4 (n is an odd integer) of a central frequency band wavelength of a leakage component of the electromagnetic wave. The leakage electromagnetic wave shielding structure according to claim 1, wherein a plurality of rubbers are embedded at a predetermined depth. 3. The leakage electromagnetic wave shielding structure according to claim 2, wherein the magnetic powder is ferrite powder. 4. When the leakage component of the electromagnetic wave is divided into a clockwise direction and a counterclockwise direction and enters the outer peripheral portion of the shield rubber fitted in the space,
The leakage electromagnetic wave shielding structure according to claim 1 or 2, wherein a distance between the electromagnetic wave input joint portion and the electromagnetic wave output joint portion of the space is set so that the electromagnetic wave leakage components have opposite phases at a composite point. .